We're going back to the moon. And we're going to the asteroids, and later, on to Mars. It's going to be exciting, and the new NASA spacecraft, Orion, seems like a very practical and efficient way to get there. But there's one problem — Orion is really cramped. Luckily, I think I have a solution.

We've known that Orion would be a smaller spacecraft than the Shuttles it's replacing — it's a capsule-type of craft as opposed to a full space plane, but the capsule design makes much more sense for the beyond-Earth-orbit missions it will be undertaking. That still doesn't change the fact that the crews of an Orion capsule will have 316 cubic feet of habitable volume to live and work in, roughly 1/8th of a shuttle orbiter's 2625 cubic feet. That's a lot less. That's moving from a McMansion in rural Iowa to a Manhattan studio.

The full impact of what this smaller working volume would mean hit me when I came across this article describing how NASA is having to re-engineer space suits for upcoming asteroid-encounter missions so that they could fit in the cramped confines of the Orion crew module. The hard-shell suits they're having to abandon may be the best suits for these sorts of missions involving lots of complex extra-vehicular activity. While I'm sure NASA can develop workable, more compact suits, I have to wonder if they even should be. Maybe the better solution is finding a way to give the Orion more usable space?

For Orion missions that are just bus rides to the ISS, the space would not be needed. And for planned long-term Mars missions, there would be a separate spacecraft with larger habitation modules to use. But that still leaves a large number of missions, including the exciting asteroid-encounter missions, with just the normal, small Orion capsule.

Redesigning the Orion capsule to be bigger is not the solution. If the capsule is made bigger and heavier, more fuel would be needed, more heat shield area, stronger parachutes, more liftoff mass, and on and on. It's too late to change the basic design of Orion, so another solution needs to be found.

Part of the solution I'll be borrowing from the Soyuz (and China's Shenzou): an orbital module. The way the Soviets (and now Russians) got around the issue of maximizing space while keeping overall mass to a minimum was to move the extra habitable volume to a separate module that would not re-enter the Earth's atmosphere.

This ovoid little Winnebago on the front of the Soyuz more than doubles the habitable volume of the spacecraft, and doesn't add much weight, because it is not intended to return to earth. That means it doesn't have to have a heat shield, doesn't have to be supported by the parachutes, and can generally be built much lighter than the return capsule.

The end result of this design approach was remarkable. The Apollo capsule designed by NASA had a mass of 5,000 kg and provided the crew with six cubic meters of living space. A service module, providing propulsion, electricity, radio, and other equipment would add at least 1,800 kg to this mass for the circumlunar mission. The Soyuz spacecraft for the same mission provided the same crew with 9 cubic meters of living space, an airlock, and the service module for the mass of the Apollo capsule alone!

And, there's other benefits, like getting a usable airlock out of the deal — essentially, you can treat the whole orbital module as an airlock and not have to vent all the air from the return capsule, which would force the whole crew into spacesuits, not just the ones actually leaving the ship.

China's Shenzou, an evolution of the Soyuz, takes the same basic approach, but has a larger, cylindrical orbital module that sports its own solar arrays and maneuvering engines, allowing it to operate independently after the rest of the Shenzou returns to earth.

The approach I'm suggesting is very similar to the Soyuz/Shenzou living module approach, but with one key difference: there's no need to launch a new one every time with every manned Orion launch.

Here's what I'm thinking: a reconfigurable mission module (based on the existing Multi-Purpose Logistics Modules or the Automated Transfer Vehicles already in use at the ISS) would be launched separately and placed into a parking orbit. After each Orion is launched, it would rendezvous and dock with the mission module, transfer equipment into it, configure it for the particular mission's needs, and then take it with them on the mission.

When the Orion returns to Earth orbit, the mission module would be stripped of any mission-specific equipment and materials, placed back into its parking orbit by Orion, and left there when Orion re-enters the atmosphere. The next Orion capsule to be launched would then be able to dock with the mission module and use it as needed.

Certain bulky equipment that is likely to be used by any Orion mission could be kept aboard the mission module, like space suits, even those big rigid ones. The mission module could have its own solar arrays and possibly maneuvering thrusters, and all of this equipment has already been developed — it's called the ATV, or Automated Transfer Vehicle.

The ATVs are currently used as resupply ships for the ISS, and they're capable of independent flight to the ISS. Their cylindrical pressurized main body contains over 1695 cubic feet of volume — over four times what the Orion module has on its own. It would not be difficult to modify the ATV into a very capable Orion mission module.

If not all of the ATV's power-generating and maneuvering capabilities are needed, the MPLV (Multi-Purpose Logistics Vehicles) could be used as well. These are similar to the ATV in that they are cargo modules, but these are just cylindrical pressurized modules, with no power or maneuvering engines. They have over 1000 cubic feet of habitable volume, and form the basis of many of the existing ISS modules, including the ESA's Columbus laboratory and the modules Tranquility and Harmony.

The ATVs are heavier and more expensive, but they do include solar panels and maneuvering engines, and I'd suspect that much of the automated docking equipment could be removed for use as an Orion mission module. MPLVs could be a simpler option, but for something that's expected to stay in a parking orbit between missions (like Shenzou's orbital module already proved it can), the ATV may be a better starting point.

The good news is both of these vehicles already exist and are proven. Modifications would need to be made, like adding a hatch so the modules could be used as airlocks and perhaps relocating heavy items like the toilet and galley from the Orion capsule, but nothing that would fundamentally change the design of the craft.

There's so many benefits to the shared mission module approach: less launch weight for the Orion itself (thanks to offloading equipment to the mission module), which would allow for larger crews and/or more fuel and supplies, better crew morale and performance on long missions because they wouldn't have to be crammed up against everyone all the time, the capsule would smell less like a porta-potty, an airlock, better spacesuits, room for more equipment/materials, and more.

Even NASA's own asteroid mission plans reflect the pains of limited space. One scenario calls for a crew of only two, both of whom would be out of the ship on EVA at the same time. NASA has never allowed that before, ever. Even Ed White's first spacewalk in 1965 on Gemini 4 left James McDivitt inside the capsule in case anything went wrong. Every spacewalk since has kept at least one crewmember inside the ship. If NASA had the extra space, they could plan on keeping this very prudent rule.

So, let's recap how this would all work for a hypothetical asteroid rendezvous mission: a mission module would have been launched prior to the main mission, with enough fuel and consumables for, say between 3-5 or so separate Orion missions. Maybe more?

The Orion spacecraft would be launched as normal, with as many crew members as the mission demands (up to six). The Orion capsule docks with the mission module in low Earth orbit, and then fires its service module engine to take it to the asteroid, likely placed somewhere in lunar orbit by a robotic probe.

The Orion and mission module go to the asteroid, some of the crew climbs out of the mission module/airlock and pokes, prods, tastes, whatever to the space rock, then they return to the airlock, divvy up their samples like Halloween candy, and prepare to return to Earth.

And, of course, all throughout the mission, they have nearly 2000 cubic feet of combined living and working space, to exercise, do experiments, eat, sleep, have clandestine space-sex, whatever.

Once back in Earth orbit, they undock from the mission module, leaving it in its parking orbit and ready for the next Orion, and they go on to re-enter, splashing back down on Earth, and planning their outfits for their parade.

It makes sense. No need to re-engineer Orion at all, just repurpose technologies we've already developed. If we're finally going to leave Earth orbit for good, we may as well do it up right, and a multi-use mission module is a way to do that.